1. Technical Field
This invention is related to a piezoelectric device and an acousto-electric transducer, and the method for manufacturing the same, which enables the characteristic frequency to be extremely higher.
2. Description of Related Art
Quartz oscillators (resonators), as one of piezoelectric devices, are used for a wide variety of application fields such as fundamental frequency generators of communication apparatus and sensing instrumentation and clock sources of general computers, office automation information equipment, home appliances, and so forth. It has been required for those characteristic frequencies to be higher by decreasing the thickness of their oscillators (resonators) in order to achieve the high performance of the information processing and transfer capabilities. Also the lens-line type finishing was proposed to produce higher quality oscillators (resonators), and these performances were accomplished for those relatively lower frequency domains.
Quartz oscillators are the essential electronic devices for digital machines such as communication equipment, computers, and so forth. It is demanded for those oscillators to increase the primary oscillation frequency by decreasing the thickness in order to achieve the high performance of the information processing and transfer abilities. Especially for mobile communication, the fundamental frequency is required to be higher for the small sizing and power saving management.
Quartz oscillators have been generally manufactured by the mechanical polishing and chemical wet etching processes. The former polishing shows the fine surface finish, however it cannot machine in lower than 30 μm. The latter etching has the advantage of decreasing deteriorated surface in principle, but it has the limitation of thickness due to the etching channel generation and so forth. On the other hand, the reactive ion etching (RIE), inductive coupled plasma etching (ICP) or plasma-etching process (abbreviated as chemical dry etching) makes the damaged surface layer, however the dry etching allows the device to be thin without the inconvenient surface roughness.
The novel mass-productive manufacturing method of high frequency quartz oscillator is developed, by combining efficiently the advantages of these processes. However the problem of reducing the thickness of those oscillators (resonators) by the dual-face polishing method (dual-face polishing machine) is presently incapable reducing the thickness to less than 30.0 μm (=55.6 MHz).
Furthermore, when oscillators were finishing in lens shape, it was extremely difficult to make the curved surface on the thin plate, and there existed no machining method of mass production with low cost.